Trouble with pattern

I am knitting a child’s sweater from lionbrand,I’m stuck on how to read
what to do next…as follows…KEEPING IN PATTERN, K14.BIND OFF NEXT 13 STS. KNIT TO END. WORKING BOTH SIDES AT ONCE. how do I knit the rest without going over the neck opening, anyone please help me
in instructions so simple to understand…this is my first big task, besides scarfs and dishclothes

You have to add a new ball of yarn.So when you knit you use one skien for one side of sts and the other skein for the next set of sts

i already cut the other strand from the second ball, can i just reattach it?

no, not if you want to work both sides at once, you could work one side with one ball, then do the other side, but really, you need to attach another ball of yarn. If you only have one ball, then wind some of it into another ball, that way you can continue as the pattern instructs.